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I installed a digital timer in a box that previously contained a switch to an outside porch light. The box has only a white, black, and ground wire. The white wire in the box is hot, not the black, as I had thought it should be.

I couldn't get the timer to work until I connected the timer's black wire to the box's white wire, the timer's red wire to the box's black wire, and the timer's white wire to the box's ground wire, along with the box's green wire to the box's bare wire.

Is this dangerous? The timer is working just fine, as described.

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2 Answers

You've created a dangerous situation. If your system is properly grounded, you likely now have current traveling across all sorts of fun things, like your gas and water pipes. If a gap develops in the grounding path, your timer might stop working till someone accidentally completes the circuit and shocks the heck out of themselves at the same time.

Disconnect the timer ASAP and wire the old switch back in. While you're at it, relabel the white wire with a bit of electrical tape or a Sharpie. Use any color other than white, gray, or green.

What you have is a switch loop. The hot loops out from the fixture, through the switch, and then comes back to the fixture to connect to neutral. A smart switch like your timer needs to use power, not just interrupt it, so it needs a neutral of its own. You need to get it that neutral; one way would be to replace the 2-wire cable coming from the existing fixture with a 3-wire cable. The fixture neutral and new cable neutral would be spliced together with the existing neutral in the fixture box. The timer switch would still be used to interrupt the path to the fixture, but it would figure out when to do so by relying on its on power.

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Yes this is bad/dangerous because you now have current running on the ground wire at all times. This type of timer requires a seperate neutral (whereas most switches just interrupt the hot) so that the timer can be powered when the switch is in the off position.

In your configuration, the line (power) comes in at the fixture and there is likely a 14/2 cable running to the switch for the sole purpose of interrupting the hot. The other configuration is where the line comes in at the switch which then sends power to the fixture when the switch is closed.

In order for you to use this type of timer, you need a dedicated neutral in the box with the switch. You would need to replace the 14/2 cable with a 14/3 cable (extra conductor) so that you can have a dedicated neutral from the line, and then still switch the hot to control the light.

Depending on the position of the switch and fixture it may be easy enough to pull a new 14/3 cable.

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